The goal of the experiments outlined in this proposal is to define the role of human Gle1p in poly (A)+ RNA nuclear export. In contrast to the nuclear import of proteins, relatively little is known about the network of factors required for RNA export. Recently, Gle1p was identified in yeast and characterized by this laboratory as the first non-RNA-binding protein necessary for poly (A) + RNA export. This protein contains a leucine-rich nuclear export signal (NES), and point mutations in this sequence alone were sufficient to inhibit mRNA export in yeast. Homology searches of the dbEST database subsequently revealed a human homologue with 54% homology to yeast Gle1p (yGle1p). Similarly to yGle1p, human Gle1p (hGle1p) localizes to the nuclear pore complex (large proteinaceous structures embedded in the nuclear envelope that serve as the gateway for movement in and out of the nucleus). Importantly, hGle1p is essential for mRNA export in vertebrate cells. However, hGle1p lacks the leucine-rich NES necessary in yGle1p for mRNA export. In addition the other previously characterized NESs are not present in hGle1p, and it was suggested that a novel NES resides in this protein. Because distinct classes of NESs likely define independent pathways for RNA export, it is possible that hGle1p is part of a novel pathway for poly (A)+ RNA export in vertebrate cells. The long-term goal of this project is to understand the molecular mechanisms underlying poly (A)+ RNA export in vertebrates. Presently, hGle1p is the only known vertebrate NES-containing, non-RNA-binding protein involved in mRNA export. The results of this study will provide a better understanding of this component of mRNA export pathway. In addition, it is likely that novel members of this pathway that associate with hGle1p will be identified and characterized, thereby further defining the mRNA export pathway in vertebrate cells. This research will significantly and importantly advance our knowledge of vertebrate mRNA export.